This invention relates to a bipolar battery plate and more particularly relates to bipolar batteries of the lead acid type and a method of making the same.
The bipolar battery has shown increasing promise for use in applications where a high rate discharge performance is required such as in the starting, lighting and ignition (SLI applications) of automobiles. The traditional lead acid batteries generally employed suffer from the characteristic ohmic resistance provided by the electrode grid, grid lug, electrode current strap, and intercell connection. Large initial drops in voltage during high rate discharge are caused by the high current densities in such components. Additionally, the components increase the battery weight considerably, an unwanted feature today with the advent of light weight automobiles. Bipolar batteries, however, because of the elimination of the components above, offer considerable advantages and have often been considered as possible replacements for traditional monopolar batteries in SLI applications.
Generally, a bipolar battery is one that has plates with positive and negative active materials adhered to respective opposite sides of the plates. The function of the bipolar plate is to allow the current to pass from one electrode to another through a conductive substrate. This eliminates the need for grid lugs, current straps and intercell connections. The available cross-sectional area for conductivity is greatly increased. Additionally, the bipolar plates can be tightly stacked against each other with suitable electrolyte present, thus occupying less space.
Many variations of bipolar plates have been designed. Some such as U.S. Pat. No. 4,124,746 issued on Nov. 7, 1978 to Nordblom, et.al. involve the use of conductive metallic plates. U.S. Pat. No. 4,525,438 issued on July 25, 1985 to Pearson describes a bipolar battery in which metallic lead expanded into grids. Others exemplified by U.S. Pat. No. 4,098,967 issued on July 4, 1978 to Biddick, et.al. teach the use of conductive plastic substrates. Such designs, however, have not resulted in a entirely satisfactory bipolar plate. Metallic substrates, while highly conductive, are significantly heavier than plastic substrates and are much more prone to corrosive attack and ultimate intercell short circuits. Conductive plastic substrates have the advantage of weighing considerably less but have less conductivity. Additionally, extremely poor adhesion often results between the plastic substrate and active material. Metallic substrates have proven only moderately more successful in this regard.